I too recommend the Ambry Genetics test for the most peace of mind since it covers so many mutations. If you ARE found to be a carrier, keep in mind that you and your boyfriend would have the following chances:
1 in 4 of having a child WITH CF
2 in 4 of having a child who is a carrier
1 in 4 of having a child who is neither a carrier nor has CF
If found to be a carrier and you still wanted to continue the process of having a biological child, your options for a 'safer' chance would be going through an in vitro fertilization clinic and doing PGD selection. The cost of this process is extremely variable between clinics, but I know at ours it would be approx. $10,000 total (meds, IVF, ICSI, PGD selection...). It is extremely unlikely that insurance would cover much, if any, of these costs.
Best wishes to your boyfriend's son.
Liz